Hot tub pergola roof

Guest User
12/30/2016
I'm replacing a roof on a pergola and would like to use metal sheets. Would would be the best option to alleviate condensation? It will be enclosed but not sealed-tight enclosed. Can I simply use some kind of vapor material over the truss and under the purlins that I'm laying the metal on? Or would you suggest laying sheathing down first? Thanks, Danna
Todd Miller
Classic Products, Inc.
12/30/2016
Condensation occurs when warm moist air hits a cool surface. What will be on the floor of the pergola? Will the area be heated ever? Generally speaking, in this situation, if condensation were to occur, a vapor barrier would just transfer the condensation from the back of the metal to the underside of the vapor barrier. Decking may be helpful. However, true "open air" structures, especially over something other than an earth floor, usually do not create situations where condensation will easily occur.
Guest User
12/30/2016
Thanks Todd, it is on a deck, with the hot tub the only item in it. the lower half of the tub is not enclosed, just the upper half with a roof and sliding cedar/plexi windows. So you dont think I'll need anything is what you're saying? Danna
Todd Miller
Classic Products, Inc.
12/30/2016
Hot tubs create a lot of moisture. I would suggest solid decking for the roof to be installed on along with underlayment.
Info @windowsonwashington.net
An informed customer is our best customer.
12/30/2016
+1 Solid decking with a nice impermeable underlayment. I would apply purlins for the roof and then the metal for an vent space above the roof for optimum venting.
Guest User
12/30/2016
So if I'm reading you both right, would it be the layers of: (top down) metal roof -> purlins->underlayment ->plywood -> truss? (see diagram) Seems like an awful lot of extra work for a 10x12 hot tub enclosure roof, but I'll do it if it means no drips in the middle of a nice soak in the winter! Thanks guys! Danna
Info @windowsonwashington.net
An informed customer is our best customer.
12/30/2016
Danna, Your order is correct. This will eliminate the condensation on the roof material. That being said, the interior surface of the roof can and will still sweat if it is cold enough. You can add insulation to the exterior for additional thermal resistance if you like for more condensation resistance.

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